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Klem H, Alegre-Requena JV, Paton RS. Catalytic Effects of Active Site Conformational Change in the Allosteric Activation of Imidazole Glycerol Phosphate Synthase. ACS Catal 2023; 13:16249-16257. [PMID: 38125975 PMCID: PMC10729027 DOI: 10.1021/acscatal.3c04176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 11/10/2023] [Accepted: 11/13/2023] [Indexed: 12/23/2023]
Abstract
Imidazole glycerol phosphate synthase (IGPS) is a class-I glutamine amidotransferase (GAT) that hydrolyzes glutamine. Ammonia is produced and transferred to a second active site, where it reacts with N1-(5'-phosphoribosyl)-formimino-5-aminoimidazole-4-carboxamide ribonucleotide (PrFAR) to form precursors to purine and histidine biosynthesis. Binding of PrFAR over 25 Å away from the active site increases glutaminase efficiency by ∼4500-fold, primarily altering the glutamine turnover number. IGPS has been the focus of many studies on allosteric communication; however, atomic details for how the glutamine hydrolysis rate increases in the presence of PrFAR are lacking. We present a density functional theory study on 237-atom active site cluster models of IGPS based on crystallized structures representing the inactive and allosterically active conformations and investigate the multistep reaction leading to thioester formation and ammonia production. The proposed mechanism is supported by similar, well-studied enzyme mechanisms, and the corresponding energy profile is consistent with steady-state kinetic studies of PrFAR + IGPS. Additional active site models are constructed to examine the relationship between active site structural change and transition-state stabilization via energy decomposition schemes. The results reveal that the inactive IGPS conformation does not provide an adequately formed oxyanion hole structure and that repositioning of the oxyanion strand relative to the substrate is vital for a catalysis-competent oxyanion hole, with or without the hVal51 dihedral flip. These findings are valuable for future endeavors in modeling the IGPS allosteric mechanism by providing insight into the atomistic changes required for rate enhancement that can inform suitable reaction coordinates for subsequent investigations.
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Affiliation(s)
- Heidi Klem
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Juan V Alegre-Requena
- Dpto.de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC, Universidad de Zaragoza, Zaragoza 50009, Spain
| | - Robert S Paton
- Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
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2
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Nakamichi Y, Kobayashi J, Toyoda K, Suda M, Hiraga K, Inui M, Watanabe M. Structural basis for the allosteric pathway of 4-amino-4-deoxychorismate synthase. Acta Crystallogr D Struct Biol 2023; 79:895-908. [PMID: 37712435 DOI: 10.1107/s2059798323006320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 07/20/2023] [Indexed: 09/16/2023] Open
Abstract
4-Amino-4-deoxychorismate synthase (ADCS), a chorismate-utilizing enzyme, is composed of two subunits: PabA and PabB. PabA is a glutamine amidotransferase that hydrolyzes glutamine into glutamate and ammonia. PabB is an aminodeoxychorismate synthase that converts chorismate to 4-amino-4-deoxychorismate (ADC) using the ammonia produced by PabA. ADCS functions under allosteric regulation between PabA and PabB. However, the allosteric mechanism remains unresolved because the structure of the PabA-PabB complex has not been determined. Here, the crystal structure and characterization of PapA from Streptomyces venezuelae (SvPapA), a bifunctional enzyme comprising the PabA and PabB domains, is reported. SvPapA forms a unique dimer in which PabA and PabB domains from different monomers complement each other and form an active structure. The chorismate-bound structure revealed that recognition of the C1 carboxyl group by Thr501 and Gly502 of the 498-PIKTG-502 motif in the PabB domain is essential for the catalytic Lys500 to reach the C2 atom, a reaction-initiation site. SvPapA demonstrated ADCS activity in the presence of Mg2+ when glutamate or NH+4 was used as the amino donor. The crystal structure indicated that the Mg2+-binding position changed depending on the binding of chorismate. In addition, significant structural changes were observed in the PabA domain depending on the presence or absence of chorismate. This study provides insights into the structural factors that are involved in the allosteric regulation of ADCS.
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Affiliation(s)
- Yusuke Nakamichi
- Research Institute for Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan
| | - Jyumpei Kobayashi
- Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
| | - Koichi Toyoda
- Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
| | - Masako Suda
- Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
| | - Kazumi Hiraga
- Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
| | - Masayuki Inui
- Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan
| | - Masahiro Watanabe
- Research Institute for Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), 3-11-32 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan
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4
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Pina AF, Sousa SF, Cerqueira NMFSA. The Catalytic Mechanism of Pdx2 Glutaminase Driven by a Cys-His-Glu Triad: A Computational Study. Chembiochem 2021; 23:e202100555. [PMID: 34762772 DOI: 10.1002/cbic.202100555] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/10/2021] [Indexed: 11/08/2022]
Abstract
The catalytic mechanism of Pdx2 was studied with atomic detail employing the computational ONIOM hybrid QM/MM methodology. Pdx2 employs a Cys-His-Glu catalytic triad to deaminate glutamine to glutamate and ammonia - the source of the nitrogen of pyridoxal 5'-phosphate (PLP). This enzyme is, therefore, a rate-limiting step in the PLP biosynthetic pathway of Malaria and Tuberculosis pathogens that rely on this mechanism to obtain PLP. For this reason, Pdx2 is considered a novel and promising drug target to treat these diseases. The results obtained show that the catalytic mechanism of Pdx2 occurs in six steps that can be divided into four stages: (i) activation of Cys87 , (ii) deamination of glutamine with the formation of the glutamyl-thioester intermediate, (iii) hydrolysis of the formed intermediate, and (iv) enzymatic turnover. The kinetic data available in the literature (19.1-19.5 kcal mol-1 ) agree very well with the calculated free energy barrier of the hydrolytic step (18.2 kcal.mol-11 ), which is the rate-limiting step of the catalytic process when substrate is readily available in the active site. This catalytic mechanism differs from other known amidases in three main points: i) it requires the activation of the nucleophile Cys87 to a thiolate; ii) the hydrolysis occurs in a single step and therefore does not require the formation of a second tetrahedral reaction intermediate, as it is proposed, and iii) Glu198 does not have a direct role in the catalytic process. Together, these results can be used for the synthesis of new transition state analogue inhibitors capable of inhibiting Pdx2 and impair diseases like Malaria and Tuberculosis.
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Affiliation(s)
- André F Pina
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal.,UCIBIO - Applied Molecular Biosciences Unit, BioSIM - Department of Biomedicine, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal
| | - Sérgio F Sousa
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal.,UCIBIO - Applied Molecular Biosciences Unit, BioSIM - Department of Biomedicine, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal
| | - Nuno M F S A Cerqueira
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal.,UCIBIO - Applied Molecular Biosciences Unit, BioSIM - Department of Biomedicine, Faculty of Medicine, University of Porto, 4200-319, Porto, Portugal
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5
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Wurm JP, Sung S, Kneuttinger AC, Hupfeld E, Sterner R, Wilmanns M, Sprangers R. Molecular basis for the allosteric activation mechanism of the heterodimeric imidazole glycerol phosphate synthase complex. Nat Commun 2021; 12:2748. [PMID: 33980881 PMCID: PMC8115485 DOI: 10.1038/s41467-021-22968-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 04/07/2021] [Indexed: 01/14/2023] Open
Abstract
Imidazole glycerol phosphate synthase (HisFH) is a heterodimeric bienzyme complex operating at a central branch point of metabolism. HisFH is responsible for the HisH-catalyzed hydrolysis of glutamine to glutamate and ammonia, which is then used for a cyclase reaction by HisF. The HisFH complex is allosterically regulated but the underlying mechanism is not well understood. Here, we elucidate the molecular basis of the long range, allosteric activation of HisFH. We establish that the catalytically active HisFH conformation is only formed when the substrates of both HisH and HisF are bound. We show that in this conformation an oxyanion hole in the HisH active site is established, which rationalizes the observed 4500-fold allosteric activation compared to the inactive conformation. In solution, the inactive and active conformations are in a dynamic equilibrium and the HisFH turnover rates correlate with the population of the active conformation, which is in accordance with the ensemble model of allostery. The allosteric regulation of the bienzyme complex imidazole glycerol phosphate synthase (HisFH) remains to be elucidated. Here, the authors provide structural insights into the dynamic allosteric mechanism by which ligand binding to the cyclase and glutaminase active sites of HisFH regulate enzyme activation.
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Affiliation(s)
- Jan Philip Wurm
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Sihyun Sung
- European Molecular Biology Laboratory, Hamburg Unit, Hamburg, Germany
| | - Andrea Christa Kneuttinger
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Enrico Hupfeld
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Reinhard Sterner
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Matthias Wilmanns
- European Molecular Biology Laboratory, Hamburg Unit, Hamburg, Germany. .,University Hamburg Clinical Center Hamburg-Eppendorf, Hamburg, Germany.
| | - Remco Sprangers
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany.
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6
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Del Caño-Ochoa F, Moreno-Morcillo M, Ramón-Maiques S. CAD, A Multienzymatic Protein at the Head of de Novo Pyrimidine Biosynthesis. Subcell Biochem 2020; 93:505-538. [PMID: 31939163 DOI: 10.1007/978-3-030-28151-9_17] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
CAD is a 1.5 MDa particle formed by hexameric association of a 250 kDa protein that carries the enzymatic activities for the first three steps in the de novo biosynthesis of pyrimidine nucleotides: glutamine-dependent Carbamoyl phosphate synthetase, Aspartate transcarbamoylase and Dihydroorotase. This metabolic pathway is essential for cell growth and proliferation and is conserved in all living organisms. However, the fusion of the first three enzymatic activities of the pathway into a single multienzymatic protein only occurs in animals. In prokaryotes, by contrast, these activities are encoded as distinct monofunctional enzymes that function independently or by forming more or less transient complexes. Whereas the structural information about these enzymes in bacteria is abundant, the large size and instability of CAD has only allowed a fragmented characterization of its structure. Here we retrace some of the most significant efforts to decipher the architecture of CAD and to understand its catalytic and regulatory mechanisms.
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Affiliation(s)
- Francisco Del Caño-Ochoa
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Nicolas Cabrera 1, 28049, Madrid, Spain
| | - María Moreno-Morcillo
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Nicolas Cabrera 1, 28049, Madrid, Spain
| | - Santiago Ramón-Maiques
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Nicolas Cabrera 1, 28049, Madrid, Spain.
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7
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Mapping the Allosteric Communication Network of Aminodeoxychorismate Synthase. J Mol Biol 2019; 431:2718-2728. [DOI: 10.1016/j.jmb.2019.05.021] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 05/10/2019] [Accepted: 05/13/2019] [Indexed: 01/31/2023]
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8
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Zhi Y, Narindoshvili T, Bogomolnaya L, Talamantes M, El Saadi A, Andrews-Polymenis H, Raushel FM. Deciphering the Enzymatic Function of the Bovine Enteric Infection-Related Protein YfeJ from Salmonella enterica Serotype Typhimurium. Biochemistry 2019; 58:1236-1245. [PMID: 30715856 DOI: 10.1021/acs.biochem.8b01283] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Non-typhoidal Salmonella can colonize the gastrointestinal system of cattle and can also cause significant food-borne disease in humans. The use of a library of single-gene deletions in Salmonella enterica serotype Typhimurium allowed identification of several proteins that are under selection in the intestine of cattle. STM2437 ( yfeJ) encodes one of these proteins, and it is currently annotated as a type I glutamine amidotransferase. STM2437 was purified to homogeneity, and its catalytic properties with a wide range of γ-glutamyl derivatives were determined. The catalytic efficiency toward the hydrolysis of l-glutamine was extremely weak with a kcat/ Km value of 20 M-1 s-1. γ-l-Glutamyl hydroxamate was identified as the best substrate for STM2437, with a kcat/ Km value of 9.6 × 104 M-1 s-1. A homology model of STM2437 was constructed on the basis of the known crystal structure of a protein of unknown function (Protein Data Bank entry 3L7N ), and γ-l-glutamyl hydroxamate was docked into the active site based on the binding of l-glutamine in the active site of carbamoyl phosphate synthetase. Acivicin was shown to inactivate the enzyme by reaction with the active site cysteine residue and the subsequent loss of HCl. Mutation of Cys91 to serine completely abolished catalytic activity. Inactivation of STM2437 did not affect the ability of this strain to colonize mice, but it inhibited the growth of S. enterica Typhimurium in bacteriologic media containing γ-l-glutamyl hydroxamate.
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Affiliation(s)
- Yuan Zhi
- Department of Biochemistry and Biophysics , Texas A&M University , College Station , Texas 77843 , United States
| | - Tamari Narindoshvili
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States
| | - Lydia Bogomolnaya
- Department of Microbial Pathogenesis and Immunology, College of Medicine , Texas A&M University System Health Science Center , Bryan , Texas 77807 , United States
| | - Marissa Talamantes
- Department of Microbial Pathogenesis and Immunology, College of Medicine , Texas A&M University System Health Science Center , Bryan , Texas 77807 , United States
| | - Ahmed El Saadi
- Department of Microbial Pathogenesis and Immunology, College of Medicine , Texas A&M University System Health Science Center , Bryan , Texas 77807 , United States
| | - Helene Andrews-Polymenis
- Department of Microbial Pathogenesis and Immunology, College of Medicine , Texas A&M University System Health Science Center , Bryan , Texas 77807 , United States
| | - Frank M Raushel
- Department of Biochemistry and Biophysics , Texas A&M University , College Station , Texas 77843 , United States.,Department of Chemistry , Texas A&M University , College Station , Texas 77843 , United States
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9
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Charlier D, Nguyen Le Minh P, Roovers M. Regulation of carbamoylphosphate synthesis in Escherichia coli: an amazing metabolite at the crossroad of arginine and pyrimidine biosynthesis. Amino Acids 2018; 50:1647-1661. [PMID: 30238253 PMCID: PMC6245113 DOI: 10.1007/s00726-018-2654-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 09/11/2018] [Indexed: 12/17/2022]
Abstract
In all organisms, carbamoylphosphate (CP) is a precursor common to the synthesis of arginine and pyrimidines. In Escherichia coli and most other Gram-negative bacteria, CP is produced by a single enzyme, carbamoylphosphate synthase (CPSase), encoded by the carAB operon. This particular situation poses a question of basic physiological interest: what are the metabolic controls coordinating the synthesis and distribution of this high-energy substance in view of the needs of both pathways? The study of the mechanisms has revealed unexpected moonlighting gene regulatory activities of enzymes and functional links between mechanisms as diverse as gene regulation and site-specific DNA recombination. At the level of enzyme production, various regulatory mechanisms were found to cooperate in a particularly intricate transcriptional control of a pair of tandem promoters. Transcription initiation is modulated by an interplay of several allosteric DNA-binding transcription factors using effector molecules from three different pathways (arginine, pyrimidines, purines), nucleoid-associated factors (NAPs), trigger enzymes (enzymes with a second unlinked gene regulatory function), DNA remodeling (bending and wrapping), UTP-dependent reiterative transcription initiation, and stringent control by the alarmone ppGpp. At the enzyme level, CPSase activity is tightly controlled by allosteric effectors originating from different pathways: an inhibitor (UMP) and two activators (ornithine and IMP) that antagonize the inhibitory effect of UMP. Furthermore, it is worth noticing that all reaction intermediates in the production of CP are extremely reactive and unstable, and protected by tunneling through a 96 Å long internal channel.
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Affiliation(s)
- Daniel Charlier
- Research Group of Microbiology, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium.
| | - Phu Nguyen Le Minh
- Research Group of Microbiology, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium
| | - Martine Roovers
- LABIRIS Institut de Recherches, Av. Emile Gryson 1, 1070, Brussels, Belgium
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10
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Leisico F, V Vieira D, Figueiredo TA, Silva M, Cabrita EJ, Sobral RG, Ludovice AM, Trincão J, Romão MJ, de Lencastre H, Santos-Silva T. First insights of peptidoglycan amidation in Gram-positive bacteria - the high-resolution crystal structure of Staphylococcus aureus glutamine amidotransferase GatD. Sci Rep 2018; 8:5313. [PMID: 29593310 PMCID: PMC5871853 DOI: 10.1038/s41598-018-22986-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 02/27/2018] [Indexed: 12/05/2022] Open
Abstract
Gram-positive bacteria homeostasis and antibiotic resistance mechanisms are dependent on the intricate architecture of the cell wall, where amidated peptidoglycan plays an important role. The amidation reaction is carried out by the bi-enzymatic complex MurT-GatD, for which biochemical and structural information is very scarce. In this work, we report the first crystal structure of the glutamine amidotransferase member of this complex, GatD from Staphylococcus aureus, at 1.85 Å resolution. A glutamine molecule is found close to the active site funnel, hydrogen-bonded to the conserved R128. In vitro functional studies using 1H-NMR spectroscopy showed that S. aureus MurT-GatD complex has glutaminase activity even in the absence of lipid II, the MurT substrate. In addition, we produced R128A, C94A and H189A mutants, which were totally inactive for glutamine deamidation, revealing their essential role in substrate sequestration and catalytic reaction. GatD from S. aureus and other pathogenic bacteria share high identity to enzymes involved in cobalamin biosynthesis, which can be grouped in a new sub-family of glutamine amidotransferases. Given the ubiquitous presence of GatD, these results provide significant insights into the molecular basis of the so far undisclosed amidation mechanism, contributing to the development of alternative therapeutics to fight infections.
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Affiliation(s)
- Francisco Leisico
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | - Diana V Vieira
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
- Oxford Protein Production Facility, Research Complex at Harwell, Didcot, United Kingdom
| | - Teresa A Figueiredo
- UCIBIO, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
- Laboratory of Molecular Genetics, Microbiology of Human Pathogens Unit, Instituto de Tecnologia Química e Biológica António Xavier da Universidade Nova de Lisboa, Oeiras, Portugal
| | - Micael Silva
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | - Eurico J Cabrita
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | - Rita G Sobral
- UCIBIO, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | - Ana Madalena Ludovice
- UCIBIO, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | | | - Maria João Romão
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
| | - Hermínia de Lencastre
- Laboratory of Molecular Genetics, Microbiology of Human Pathogens Unit, Instituto de Tecnologia Química e Biológica António Xavier da Universidade Nova de Lisboa, Oeiras, Portugal.
- Laboratory of Microbiology and Infectious Diseases, The Rockefeller University, New York, USA.
| | - Teresa Santos-Silva
- UCIBIO, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal.
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11
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Sanyal N, Arentson BW, Luo M, Tanner JJ, Becker DF. First evidence for substrate channeling between proline catabolic enzymes: a validation of domain fusion analysis for predicting protein-protein interactions. J Biol Chem 2014; 290:2225-34. [PMID: 25492892 DOI: 10.1074/jbc.m114.625483] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Proline dehydrogenase (PRODH) and Δ(1)-pyrroline-5-carboxylate (P5C) dehydrogenase (P5CDH) catalyze the four-electron oxidation of proline to glutamate via the intermediates P5C and l-glutamate-γ-semialdehyde (GSA). In Gram-negative bacteria, PRODH and P5CDH are fused together in the bifunctional enzyme proline utilization A (PutA) whereas in other organisms PRODH and P5CDH are expressed as separate monofunctional enzymes. Substrate channeling has previously been shown for bifunctional PutAs, but whether the monofunctional enzymes utilize an analogous channeling mechanism has not been examined. Here, we report the first evidence of substrate channeling in a PRODH-P5CDH two-enzyme pair. Kinetic data for the coupled reaction of PRODH and P5CDH from Thermus thermophilus are consistent with a substrate channeling mechanism, as the approach to steady-state formation of NADH does not fit a non-channeling two-enzyme model. Furthermore, inactive P5CDH and PRODH mutants inhibit NADH production and increase trapping of the P5C intermediate in coupled assays of wild-type PRODH-P5CDH enzyme pairs, indicating that the mutants disrupt PRODH-P5CDH channeling interactions. A dissociation constant of 3 μm was estimated for a putative PRODH-P5CDH complex by surface plasmon resonance (SPR). Interestingly, P5CDH binding to PRODH was only observed when PRODH was immobilized with the top face of its (βα)8 barrel exposed. Using the known x-ray crystal structures of PRODH and P5CDH from T. thermophilus, a model was built for a proposed PRODH-P5CDH enzyme channeling complex. The structural model predicts that the core channeling pathway of bifunctional PutA enzymes is conserved in monofunctional PRODH-P5CDH enzyme pairs.
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Affiliation(s)
- Nikhilesh Sanyal
- From the Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 and
| | - Benjamin W Arentson
- From the Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 and
| | - Min Luo
- Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
| | - John J Tanner
- Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211 the Departments of Biochemistry and
| | - Donald F Becker
- From the Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 and
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12
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Arentson B, Luo M, Pemberton TA, Tanner JJ, Becker DF. Kinetic and structural characterization of tunnel-perturbing mutants in Bradyrhizobium japonicum proline utilization A. Biochemistry 2014; 53:5150-61. [PMID: 25046425 PMCID: PMC4131897 DOI: 10.1021/bi5007404] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 07/18/2014] [Indexed: 01/09/2023]
Abstract
Proline utilization A from Bradyrhizobium japonicum (BjPutA) is a bifunctional flavoenzyme that catalyzes the oxidation of proline to glutamate using fused proline dehydrogenase (PRODH) and Δ(1)-pyrroline-5-carboxylate dehydrogenase (P5CDH) domains. Recent crystal structures and kinetic data suggest an intramolecular channel connects the two active sites, promoting substrate channeling of the intermediate Δ(1)-pyrroline-5-carboxylate/glutamate-γ-semialdehyde (P5C/GSA). In this work, the structure of the channel was explored by inserting large side chain residues at four positions along the channel in BjPutA. Kinetic analysis of the different mutants revealed replacement of D779 with Tyr (D779Y) or Trp (D779W) significantly decreased the overall rate of the PRODH-P5CDH channeling reaction. X-ray crystal structures of D779Y and D779W revealed that the large side chains caused a constriction in the central section of the tunnel, thus likely impeding the travel of P5C/GSA in the channel. The D779Y and D779W mutants have PRODH activity similar to that of wild-type BjPutA but exhibit significantly lower P5CDH activity, suggesting that exogenous P5C/GSA enters the channel upstream of Asp779. Replacement of nearby Asp778 with Tyr (D778Y) did not impact BjPutA channeling activity. Consistent with the kinetic results, the X-ray crystal structure of D778Y shows that the main channel pathway is not impacted; however, an off-cavity pathway is closed off from the channel. These findings provide evidence that the off-cavity pathway is not essential for substrate channeling in BjPutA.
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Affiliation(s)
- Benjamin
W. Arentson
- Department
of Biochemistry, Redox Biology Center, University
of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States
| | - Min Luo
- Departments of Biochemistry and Chemistry, University
of Missouri—Columbia, Columbia, Missouri 65211, United States
| | - Travis A. Pemberton
- Departments of Biochemistry and Chemistry, University
of Missouri—Columbia, Columbia, Missouri 65211, United States
| | - John J. Tanner
- Departments of Biochemistry and Chemistry, University
of Missouri—Columbia, Columbia, Missouri 65211, United States
| | - Donald F. Becker
- Department
of Biochemistry, Redox Biology Center, University
of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States
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13
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Analyses of cobalt-ligand and potassium-ligand bond lengths in metalloproteins: trends and patterns. J Mol Model 2014; 20:2271. [PMID: 24850495 DOI: 10.1007/s00894-014-2271-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Accepted: 04/23/2014] [Indexed: 10/25/2022]
Abstract
Cobalt and potassium are biologically important metal elements that are present in a large array of proteins. Cobalt is mostly found in vivo associated with a corrin ring, which represents the core of the vitamin B12 molecule. Potassium is the most abundant metal in the cytosol, and it plays a crucial role in maintaining membrane potential as well as correct protein function. Here, we report a thorough analysis of the geometric properties of cobalt and potassium coordination spheres that was performed with high resolution on a representative set of structures from the Protein Data Bank and complemented by quantum mechanical calculations realized at the DFT level of theory (B3LYP/ SDD) on mononuclear model systems. The results allowed us to draw interesting conclusions on the structural characteristics of both Co and K centers, and to evaluate the importance of effects such as their association energies and intrinsic thermodynamic stabilities. Overall, the results obtained provide useful data for enhancing the atomic models normally applied in theoretical and computational studies of Co or K proteins performed at the quantum mechanical level, and for developing molecular mechanical parameters for treating Co or K coordination spheres in molecular mechanics or molecular dynamics studies.
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14
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Tanwar AS, Goyal VD, Choudhary D, Panjikar S, Anand R. Importance of hydrophobic cavities in allosteric regulation of formylglycinamide synthetase: insight from xenon trapping and statistical coupling analysis. PLoS One 2013; 8:e77781. [PMID: 24223728 PMCID: PMC3815217 DOI: 10.1371/journal.pone.0077781] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 09/12/2013] [Indexed: 11/19/2022] Open
Abstract
Formylglycinamide ribonucleotide amidotransferase (FGAR-AT) is a 140 kDa bi-functional enzyme involved in a coupled reaction, where the glutaminase active site produces ammonia that is subsequently utilized to convert FGAR to its corresponding amidine in an ATP assisted fashion. The structure of FGAR-AT has been previously determined in an inactive state and the mechanism of activation remains largely unknown. In the current study, hydrophobic cavities were used as markers to identify regions involved in domain movements that facilitate catalytic coupling and subsequent activation of the enzyme. Three internal hydrophobic cavities were located by xenon trapping experiments on FGAR-AT crystals and further, these cavities were perturbed via site-directed mutagenesis. Biophysical characterization of the mutants demonstrated that two of these three voids are crucial for stability and function of the protein, although being ∼20 Å from the active centers. Interestingly, correlation analysis corroborated the experimental findings, and revealed that amino acids lining the functionally important cavities form correlated sets (co-evolving residues) that connect these regions to the amidotransferase active center. It was further proposed that the first cavity is transient and allows for breathing motion to occur and thereby serves as an allosteric hotspot. In contrast, the third cavity which lacks correlated residues was found to be highly plastic and accommodated steric congestion by local adjustment of the structure without affecting either stability or activity.
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Affiliation(s)
- Ajay Singh Tanwar
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, India
| | - Venuka Durani Goyal
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, India
| | - Deepanshu Choudhary
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, India
| | - Santosh Panjikar
- Australian Synchrotron, Clayton, Australia
- Department of Biochemistry and Molecular Biology, Monash University, Victoria, Australia
| | - Ruchi Anand
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, India
- * E-mail:
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15
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Chuankhayan P, Kao TT, Lin CC, Guan HH, Nakagawa A, Fu TF, Chen CJ. Structural Insights into the Hydrolysis and Polymorphism of Methotrexate Polyglutamate by Zebrafish γ-Glutamyl Hydrolase. J Med Chem 2013; 56:7625-35. [DOI: 10.1021/jm401013e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Phimonphan Chuankhayan
- Life
Science Group, Scientific Research
Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Tseng-Ting Kao
- Department of Medical Laboratory Science
and Biotechnology, College of
Medicine, National Cheng Kung University, Tainan 701, Taiwan
| | - Chien-Chih Lin
- Life
Science Group, Scientific Research
Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Hong-Hsiang Guan
- Life
Science Group, Scientific Research
Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Atsushi Nakagawa
- Institute
for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Tzu-Fun Fu
- Department of Medical Laboratory Science
and Biotechnology, College of
Medicine, National Cheng Kung University, Tainan 701, Taiwan
| | - Chun-Jung Chen
- Life
Science Group, Scientific Research
Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
- Department
of Physics, National Tsing Hua University, Hsinchu 30043, Taiwan
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16
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List F, Vega M, Razeto A, Häger M, Sterner R, Wilmanns M. Catalysis Uncoupling in a Glutamine Amidotransferase Bienzyme by Unblocking the Glutaminase Active Site. ACTA ACUST UNITED AC 2012; 19:1589-99. [DOI: 10.1016/j.chembiol.2012.10.012] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2012] [Revised: 10/02/2012] [Accepted: 10/11/2012] [Indexed: 11/30/2022]
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17
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Arentson BW, Sanyal N, Becker DF. Substrate channeling in proline metabolism. Front Biosci (Landmark Ed) 2012; 17:375-88. [PMID: 22201749 DOI: 10.2741/3932] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Proline metabolism is an important pathway that has relevance in several cellular functions such as redox balance, apoptosis, and cell survival. Results from different groups have indicated that substrate channeling of proline metabolic intermediates may be a critical mechanism. One intermediate is pyrroline-5-carboxylate (P5C), which upon hydrolysis opens to glutamic semialdehyde (GSA). Recent structural and kinetic evidence indicate substrate channeling of P5C/GSA occurs in the proline catabolic pathway between the proline dehydrogenase and P5C dehydrogenase active sites of bifunctional proline utilization A (PutA). Substrate channeling in PutA is proposed to facilitate the hydrolysis of P5C to GSA which is unfavorable at physiological pH. The second intermediate, gamma-glutamyl phosphate, is part of the proline biosynthetic pathway and is extremely labile. Substrate channeling of gamma-glutamyl phosphate is thought to be necessary to protect it from bulk solvent. Because of the unfavorable equilibrium of P5C/GSA and the reactivity of gamma-glutamyl phosphate, substrate channeling likely improves the efficiency of proline metabolism. Here, we outline general strategies for testing substrate channeling and review the evidence for channeling in proline metabolism.
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Affiliation(s)
- Benjamin W Arentson
- Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
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18
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Lund L, Fan Y, Shao Q, Gao YQ, Raushel FM. Carbamate transport in carbamoyl phosphate synthetase: a theoretical and experimental investigation. J Am Chem Soc 2010; 132:3870-8. [PMID: 20187643 DOI: 10.1021/ja910441v] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The transport of carbamate through the large subunit of carbamoyl phosphate synthetase (CPS) from Escherichia coli was investigated by molecular dynamics and site-directed mutagenesis. Carbamate, the product of the reaction involving ATP, bicarbonate, and ammonia, must be delivered from the site of formation to the site of utilization by traveling nearly 40 A within the enzyme. Potentials of mean force (PMF) calculations along the entire tunnel for the translocation of carbamate indicate that the tunnel is composed of three continuous water pockets and two narrow connecting parts, near Ala-23 and Gly-575. The two narrow parts render two free energy barriers of 6.7 and 8.4 kcal/mol, respectively. Three water pockets were filled with about 21, 9, and 9 waters, respectively, and the corresponding relative free energies of carbamate residing in these free energy minima are 5.8, 0, and 1.6 kcal/mol, respectively. The release of phosphate into solution at the site for the formation of carbamate allows the side chain of Arg-306 to rotate toward Glu-25, Glu-383, and Glu-604. This rotation is virtually prohibited by a barrier of at least 23 kcal/mol when phosphate remains bound. This conformational change not only opens the entrance of the tunnel but also shields the charge-charge repulsion from the three glutamate residues when carbamate passes through the tunnel. Two mutants, A23F and G575F, were designed to block the migration of carbamate through the narrowest parts of the carbamate tunnel. The mutants retained only 1.7% and 3.8% of the catalytic activity for the synthesis of carbamoyl phosphate relative to the wild type CPS, respectively.
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Affiliation(s)
- Liliya Lund
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA
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19
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Fan Y, Lund L, Shao Q, Gao YQ, Raushel FM. A combined theoretical and experimental study of the ammonia tunnel in carbamoyl phosphate synthetase. J Am Chem Soc 2009; 131:10211-9. [PMID: 19569682 DOI: 10.1021/ja902557r] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The transfer of ammonia in carbamoyl phosphate synthetase (CPS) was investigated by molecular dynamics simulations and experimental characterization of mutations within the ammonia tunnel. In CPS, ammonia is derived from the hydrolysis of glutamine and this intermediate must travel approximately 45 A from the site of formation in the small subunit to the site of utilization in the large subunit. In this investigation, the migration of ammonia was analyzed from the exit of the small subunit through the large subunit where it ultimately reacts with the carboxy phosphate intermediate. Potential of mean force calculations along the transfer pathway for ammonia indicate a relatively low free-energy barrier for the translocation of ammonia. The highest barrier of 7.2 kcal/mol is found at a narrow turning gate surrounded by the side chains of Cys-232, Ala-251, and Ala-314 in the large subunit. The environment of the ammonia tunnel from the exit of the small subunit to the turning gate in the tunnel is filled with clusters of water molecules and the ammonia is able to travel through this area easily. After ammonia passes through the turning gate, it enters a hydrophobic passage. A hydrogen bond then forms between the ammonia and Thr-249, which facilitates the delivery to a more hydrophilic environment near the active site for the reaction with the carboxy phosphate intermediate. The transport process from the turning gate to the end of the tunnel is favored by an overall downhill free-energy potential and no free-energy barrier higher than 3 kcal/mol. A conformational change of the turning gate, caused by formation of the carboxy phosphate intermediate, is consistent with a mechanism in which the reaction between ATP and bicarbonate triggers the transport of ammonia and consequently accelerates the rate of glutamine hydrolysis in the small subunit. A blockage in the turning gate passageway was introduced by the triple mutant C232V/A251V/A314V. This mutant is unable to synthesize carbamoyl phosphate using glutamine as a nitrogen source.
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Affiliation(s)
- Yubo Fan
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
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20
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Xiang DF, Kolb P, Fedorov AA, Meier MM, Fedorov EV, Nguyen TT, Sterner R, Almo SC, Shoichet BK, Raushel FM. Functional annotation and three-dimensional structure of Dr0930 from Deinococcus radiodurans, a close relative of phosphotriesterase in the amidohydrolase superfamily. Biochemistry 2009; 48:2237-47. [PMID: 19159332 PMCID: PMC3176505 DOI: 10.1021/bi802274f] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dr0930, a member of the amidohydrolase superfamily in Deinococcus radiodurans, was cloned, expressed, and purified to homogeneity. The enzyme crystallized in the space group P3121, and the structure was determined to a resolution of 2.1 A. The protein folds as a (beta/alpha)7beta-barrel, and a binuclear metal center is found at the C-terminal end of the beta-barrel. The purified protein contains a mixture of zinc and iron and is intensely purple at high concentrations. The purple color was determined to be due to a charge transfer complex between iron in the beta-metal position and Tyr-97. Mutation of Tyr-97 to phenylalanine or complexation of the metal center with manganese abolished the absorbance in the visible region of the spectrum. Computational docking was used to predict potential substrates for this previously unannotated protein. The enzyme was found to catalyze the hydrolysis of delta- and gamma-lactones with an alkyl substitution at the carbon adjacent to the ring oxygen. The best substrate was delta-nonanoic lactone with a kcat/Km of 1.6 x 10(6) M-1 s-1. Dr0930 was also found to catalyze the very slow hydrolysis of paraoxon with values of kcat and kcat/Km of 0.07 min-1 and 0.8 M-1 s-1, respectively. The amino acid sequence identity to the phosphotriesterase (PTE) from Pseudomonas diminuta is 30%. The eight substrate specificity loops were transplanted from PTE to Dr0930, but no phosphotriesterase activity could be detected in the chimeric PTE-Dr0930 hybrid. Mutation of Phe-26 and Cys-72 in Dr0930 to residues found in the active site of PTE enhanced the kinetic constants for the hydrolysis of paraoxon. The F26G/C72I mutant catalyzed the hydrolysis of paraoxon with a kcat of 1.14 min-1, an increase of 16-fold over the wild-type enzyme. These results support previous proposals that phosphotriesterase activity evolved from an ancestral parent enzyme possessing lactonase activity.
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Affiliation(s)
- Dao Feng Xiang
- Department of Chemistry, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012
| | - Peter Kolb
- Department of Pharmaceutical Chemistry, University of California, San Francisco, MC 2550 1700 4 Street, San Francisco, California 94158-2330
| | - Alexander A. Fedorov
- Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461
| | - Monika M. Meier
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstrasse 31, D93053 Regensburg, Germany
| | - Elena V. Fedorov
- Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461
| | - Tinh T. Nguyen
- Department of Chemistry, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012
| | - Reinhard Sterner
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstrasse 31, D93053 Regensburg, Germany
| | - Steven C. Almo
- Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461
| | - Brian K. Shoichet
- Department of Pharmaceutical Chemistry, University of California, San Francisco, MC 2550 1700 4 Street, San Francisco, California 94158-2330
| | - Frank M. Raushel
- Department of Chemistry, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012
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21
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Genetic identification of essential indels and domains in carbamoyl phosphate synthetase II of Toxoplasma gondii. Int J Parasitol 2008; 39:533-9. [PMID: 18992249 DOI: 10.1016/j.ijpara.2008.09.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 09/16/2008] [Accepted: 09/17/2008] [Indexed: 11/23/2022]
Abstract
New treatments need to be developed for the significant human diseases of toxoplasmosis and malaria to circumvent problems with current treatments and drug resistance. Apicomplexan parasites causing these lethal diseases are deficient in pyrimidine salvage, suggesting that selective inhibition of de novo pyrimidine biosynthesis can lead to a severe loss of uridine 5'-monophosphate (UMP) and thymidine 5'-monophosphate (dTMP) pools, thereby inhibiting parasite RNA and DNA synthesis. Disruption of Toxoplasma gondii carbamoyl phosphate synthetase II (CPSII) induces a severe uracil auxotrophy with no detectable parasite replication in vitro and complete attenuation of virulence in mice. Here we show that a CPSII cDNA minigene efficiently complements the uracil auxotrophy of CPSII-deficient mutants, restoring parasite growth and virulence. Our complementation assays reveal that engineered mutations within, or proximal to, the catalytic triad of the N-terminal glutamine amidotransferase (GATase) domain inactivate the complementation activity of T. gondii CPSII and demonstrate a critical dependence on the apicomplexan CPSII GATase domain in vivo. Surprisingly, indels present within the T. gondii CPSII GATase domain as well as the C-terminal allosteric regulatory domain are found to be essential. In addition, several mutations directed at residues implicated in allosteric regulation in Escherichia coli CPS either abolish or markedly suppress complementation and further define the functional importance of the allosteric regulatory region. Collectively, these findings identify novel features of T. gondii CPSII as potential parasite-selective targets for drug development.
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22
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Morar M, Hoskins AA, Stubbe J, Ealick SE. Formylglycinamide ribonucleotide amidotransferase from Thermotoga maritima: structural insights into complex formation. Biochemistry 2008; 47:7816-30. [PMID: 18597481 PMCID: PMC2646663 DOI: 10.1021/bi800329p] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the fourth step of the purine biosynthetic pathway, formyl glycinamide ribonucleotide (FGAR) amidotransferase, also known as PurL, catalyzes the conversion of FGAR, ATP, and glutamine to formyl glycinamidine ribonucleotide (FGAM), ADP, P i, and glutamate. Two forms of PurL have been characterized, large and small. Large PurL, present in most Gram-negative bacteria and eukaryotes, consists of a single polypeptide chain and contains three major domains: the N-terminal domain, the FGAM synthetase domain, and the glutaminase domain, with a putative ammonia channel located between the active sites of the latter two. Small PurL, present in Gram-positive bacteria and archaea, is structurally homologous to the FGAM synthetase domain of large PurL, and forms a complex with two additional gene products, PurQ and PurS. The structure of the PurS dimer is homologous with the N-terminal domain of large PurL, while PurQ, whose structure has not been reported, contains the glutaminase activity. In Bacillus subtilis, the formation of the PurLQS complex is dependent on glutamine and ADP and has been demonstrated by size-exclusion chromatography. In this work, a structure of the PurLQS complex from Thermotoga maritima is described revealing a 2:1:1 stoichiometry of PurS:Q:L, respectively. The conformational changes observed in TmPurL upon complex formation elucidate the mechanism of metabolite-mediated recruitment of PurQ and PurS. The flexibility of the PurS dimer is proposed to play a role in the activation of the complex and the formation of the ammonia channel. A potential path for the ammonia channel is identified.
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Affiliation(s)
- Mariya Morar
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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23
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Hart EJ, Powers-Lee SG. Mutation analysis of carbamoyl phosphate synthetase: does the structurally conserved glutamine amidotransferase triad act as a functional dyad? Protein Sci 2008; 17:1120-8. [PMID: 18458150 DOI: 10.1110/ps.073428008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Evolutionarily conserved triad glutamine amidotransferase (GAT) domains catalyze the cleavage of glutamine to yield ammonia and sequester the ammonia in a tunnel until delivery to a variety of acceptor substrates in synthetase domains of variable structure. Whereas a conserved hydrolytic triad (Cys/His/Glu) is observed in the solved GAT structures, the specificity pocket for glutamine is not apparent, presumably because its formation is dependent on the conformational change that couples acceptor availability to a greatly increased rate of glutamine cleavage. In Escherichia coli carbamoyl phosphate synthetase (eCPS), one of the best characterized triad GAT members, the Cys269 and His353 triad residues are essential for glutamine hydrolysis, whereas Glu355 is not critical for eCPS activity. To further define the glutamine-binding pocket and possibly identify an alternative member of the catalytic triad that is situated for this role in the coupled conformation, we have analyzed mutations at Gln310, Asn311, Asp334, and Gln351, four conserved, but not yet analyzed residues that might potentially function as the third triad member. Alanine substitution of Gln351, Asn311, and Gln310 yielded respective K(m) increases of 145, 27, and 15, suggesting that Gln351 plays a key role in glutamine binding in the coupled conformation, and that Asn311 and Gln310 make less significant contributions. None of the mutant k (cat) values varied significantly from those for wild-type eCPS. Combined with previously reported data on other conserved eCPS residues, these results strongly suggest that Cys269 and His353 function as a catalytic dyad in the GAT site of eCPS.
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Affiliation(s)
- Emily J Hart
- Department of Biology, Northeastern University, Boston, Massachusetts 02115-5000, USA
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24
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Fan Y, Lund L, Yang L, Raushel FM, Gao YQ. Mechanism for the Transport of Ammonia within Carbamoyl Phosphate Synthetase Determined by Molecular Dynamics Simulations. Biochemistry 2008; 47:2935-44. [DOI: 10.1021/bi701572h] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yubo Fan
- Department of Chemistry, Texas A&M University, College Station, Texas 77843
| | - Liliya Lund
- Department of Chemistry, Texas A&M University, College Station, Texas 77843
| | - Lijiang Yang
- Department of Chemistry, Texas A&M University, College Station, Texas 77843
| | - Frank M. Raushel
- Department of Chemistry, Texas A&M University, College Station, Texas 77843
| | - Yi-Qin Gao
- Department of Chemistry, Texas A&M University, College Station, Texas 77843
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25
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Mouilleron S, Golinelli-Pimpaneau B. Conformational changes in ammonia-channeling glutamine amidotransferases. Curr Opin Struct Biol 2007; 17:653-64. [PMID: 17951049 DOI: 10.1016/j.sbi.2007.09.003] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 09/04/2007] [Accepted: 09/06/2007] [Indexed: 11/28/2022]
Abstract
Glutamine amidotransferases (GATs), which catalyze the synthesis of different aminated products, channel ammonia over 10-40 A from a glutamine substrate at the glutaminase site to an acceptor substrate at the synthase site. Ammonia production usually uses a cysteine-histidine-glutamate triad or a N-terminal cysteine residue. Crystal structures of several amidotransferase ligand complexes, mimicking intermediates along the catalytic cycle, have now been determined. In most cases, acceptor binding triggers glutaminase activation through domain-hinged movements and other conformational changes. Structural information shows how flexible loops of the synthase and glutaminase domains move to shield the two catalytic sites and anchor the substrates, and how the ammonia channel forms and opens or closes.
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Affiliation(s)
- Stéphane Mouilleron
- Laboratoire d'Enzymologie et Biochimie structurales, CNRS Bâtiment 34, 1 avenue de la Terrasse, 91190 Gif-sur-Yvette, France
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26
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Johnson JL, West JK, Nelson ADL, Reinhart GD. Resolving the fluorescence response of Escherichia coli carbamoyl phosphate synthetase: mapping intra- and intersubunit conformational changes. Biochemistry 2007; 46:387-97. [PMID: 17209549 PMCID: PMC2559813 DOI: 10.1021/bi061642n] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Carbamoyl phosphate synthetase (CPS) from Escherichia coli is potentially overlaid with a network of allosterism, interconnecting active sites, effector binding sites, and aggregate interfaces to control its mechanisms of catalytic synchronization, regulation, and oligomerization, respectively. To characterize these conformational changes, a tryptophan-free variant of CPS was genetically engineered by substituting six native tryptophans with tyrosines. Each tryptophan was then reinserted, singly, as a specific fluorescence probe of its corresponding microenvironment. The amino acid substitutions themselves result in little apparent disruption of the protein; variants maintain catalytic and allosteric functionality, and the fluorescence properties of each tryptophan, while unique, are additive to wild-type CPS. Whereas the collective, intrinsic fluorescence response of E. coli CPS is largely insensitive to ligand binding, changes of the individual probes in intensity, lifetime, anisotropy, and accessibility to acrylamide quenching highlight the dynamic interplay between several protein domains, as well as between subunits. W213 within the carboxy phosphate domain, for example, exhibits an almost 40% increase in intensity upon saturation with ATP; W437 of the oligomerization domain, in contrast, is essentially silent in its fluorescence to the binding of ligands. Nucleotide and bicarbonate association within the large subunit induces fluorescence changes in both W170 and W175 of the small subunit, indicative of the type of long-range interactions purportedly synchronizing the carboxy phosphate and amidotransferase domains of the enzyme to initiate catalysis. ATP and ADP engender different fluorescence responses in most tryptophans, perhaps reflecting coordinating, conformational changes accompanying the cycling of reactants and products during catalysis.
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Affiliation(s)
- Jason L. Johnson
- Corresponding authors. Phone: (580) 774−3110, Fax: (580) 774−3115, E-mail: (JLJ); or Phone: (979) 862−2263, Fax: (979) 845−4295, E-mail: (GDR)
| | | | | | - Gregory D. Reinhart
- Corresponding authors. Phone: (580) 774−3110, Fax: (580) 774−3115, E-mail: (JLJ); or Phone: (979) 862−2263, Fax: (979) 845−4295, E-mail: (GDR)
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27
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Ihara H, Ikeda Y, Toma S, Wang X, Suzuki T, Gu J, Miyoshi E, Tsukihara T, Honke K, Matsumoto A, Nakagawa A, Taniguchi N. Crystal structure of mammalian α1,6-fucosyltransferase, FUT8. Glycobiology 2006; 17:455-66. [PMID: 17172260 DOI: 10.1093/glycob/cwl079] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mammalian alpha1,6-fucosyltransferase (FUT8) catalyses the transfer of a fucose residue from a donor substrate, guanosine 5'-diphosphate-beta-L-fucose to the reducing terminal N-acetylglucosamine (GlcNAc) of the core structure of an asparagine-linked oligosaccharide. Alpha1,6-fucosylation, also referred to as core fucosylation, plays an essential role in various pathophysiological events. Our group reported that FUT8 null mice showed severe growth retardation and emphysema-like lung-destruction as a result of the dysfunction of epidermal growth factor and transforming growth factor-beta receptors. To elucidate the molecular basis of FUT8 with respect to pathophysiology, the crystal structure of human FUT8 was determined at 2.6 A resolution. The overall structure of FUT8 was found to consist of three domains: an N-terminal coiled-coil domain, a catalytic domain, and a C-terminal SH3 domain. The catalytic region appears to be similar to GT-B glycosyltransferases rather than GT-A. The C-terminal part of the catalytic domain of FUT8 includes a Rossmann fold with three regions that are conserved in alpha1,6-, alpha1,2-, and protein O-fucosyltransferases. The SH3 domain of FUT8 is similar to other SH3 domain-containing proteins, although the significance of this domain remains to be elucidated. The present findings of FUT8 suggest that the conserved residues in the three conserved regions participate in the Rossmann fold and act as the donor binding site, or in catalysis, thus playing key roles in the fucose-transferring reaction.
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Affiliation(s)
- Hideyuki Ihara
- Department of Disease Glycomics, Research Institute for Microbial Diseases, Osaka University, Taniguchi Research Group, 4th Floor, Center for Advanced Science & Innovation, Osaka University, 2-1, Yamadaoka Suita, Osaka 565-0871, Japan
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Slocum RD. Genes, enzymes and regulation of arginine biosynthesis in plants. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2005; 43:729-45. [PMID: 16122935 DOI: 10.1016/j.plaphy.2005.06.007] [Citation(s) in RCA: 184] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Accepted: 06/17/2005] [Indexed: 05/04/2023]
Abstract
Arabidopsis genes encoding enzymes for each of the eight steps in L-arginine (Arg) synthesis were identified, based upon sequence homologies with orthologs from other organisms. Except for N-acetylglutamate synthase (NAGS; EC 2.3.1.1), which is encoded by two genes, all remaining enzymes are encoded by single genes. Targeting predictions for these enzymes, based upon their deduced sequences, and subcellular fractionation studies, suggest that most enzymes of Arg synthesis reside within the plastid. Synthesis of the L-ornthine (Orn) intermediate in this pathway from L-glutamate occurs as a series of acetylated intermediates, as in most other organisms. An N-acetylornithine:glutamate acetyltransferase (NAOGAcT; EC 2.3.1.35) facilitates recycling of the acetyl moiety during Orn formation (cyclic pathway). A putative N-acetylornithine deacetylase (NAOD; EC 3.5.1.16), which participates in the "linear" pathway for Orn synthesis in some organisms, was also identified. Previous biochemical studies have indicated that allosteric regulation of the first and, especially, the second steps in Orn synthesis (NAGS; N-acetylglutamate kinase (NAGK), EC 2.7.2.8) by the Arg end-product are the major sites of metabolic control of the pathway in organisms using the cyclic pathway. Gene expression profiling for pathway enzymes further suggests that NAGS, NAGK, NAOGAcT and NAOD are coordinately regulated in response to changes in Arg demand during plant growth and development. Synthesis of Arg from Orn is further coordinated with pyrimidine nucleotide synthesis, at the level of allocation of the common carbamoyl-P intermediate.
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Affiliation(s)
- Robert D Slocum
- Department of Biological Sciences, Goucher College, Baltimore, MD 21204-2794, USA.
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29
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Raschle T, Amrhein N, Fitzpatrick TB. On the two components of pyridoxal 5'-phosphate synthase from Bacillus subtilis. J Biol Chem 2005; 280:32291-300. [PMID: 16030023 DOI: 10.1074/jbc.m501356200] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Vitamin B6 is an essential nutrient in the human diet. It can act as a co-enzyme for numerous metabolic enzymes and has recently been shown to be a potent antioxidant. Plants and microorganisms have the ability to make the compound. Yet, studies of vitamin B6 biosynthesis have been mainly restricted to Escherichia coli, where the vitamin is synthesized from 1-deoxy-d -xylulose 5-phosphate and 4-phosphohydroxy-l-threonine. Recently, a novel pathway for its synthesis has been discovered, involving two genes (PDX1 and PDX2) neither of which is homologous to any of those participating in the E. coli pathway. In Bacillus subtilis, YaaD and YaaE represent the PDX1 and PDX2 homolog, respectively. The two proteins form a complex that functions as a glutamine amidotransferase, with YaaE as the glutaminase domain and YaaD as the acceptor and pyridoxal 5'-phosphate (PLP) synthesis domain. In this report we corroborate a recent report on the identification of the substrates of YaaD and provide unequivocal proof of the identity of the reaction product. We show that both the glutaminase and synthase reactions are dependent on the respective protein partner. The synthase reaction can also utilize an external ammonium source but, in contrast to other glutamine amidotransferases, is dependent on YaaE under certain conditions. Furthermore, we report on the detailed characterization of the inhibition of the glutaminase domain, and thus PLP synthesis, by the glutamine analog acivicin. Employing pull-out assays and native-PAGE, we provide evidence for the dissociation of the bi-enzyme complex under these conditions. The results are discussed in light of the nature of the interaction of the two components of the enzyme complex.
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Affiliation(s)
- Thomas Raschle
- ETH-Zürich, Institut für Pflanzenwissenschaften, Zürich, Switzerland
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30
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Amaro RE, Myers RS, Davisson VJ, Luthey-Schulten ZA. Structural elements in IGP synthase exclude water to optimize ammonia transfer. Biophys J 2005; 89:475-87. [PMID: 15849257 PMCID: PMC1366548 DOI: 10.1529/biophysj.104.058651] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the complex pathway of histidine biosynthesis, a key branch point linking amino acid and purine biosynthesis is catalyzed by the bifunctional enzyme imidazole glycerol phosphate (IGP) synthase. The first domain of IGP synthase, a triad glutamine amidotransferase, hydrolyzes glutamine to form glutamate and ammonia. Its activity is tightly regulated by the binding of the substrate PRFAR to its partner synthase domain. Recent crystal structures and molecular dynamics simulations strongly suggest that the synthase domain, a (beta/alpha)(8) barrel protein, mediates the insertion of ammonia and ring formation in IGP by channeling ammonia from one remote active site to the other. Here, we combine both mutagenesis experiments and computational investigations to gain insight into the transfer of ammonia and the mechanism of conduction. We discover an alternate route for the entrance of ammonia into the (beta/alpha)(8) barrel and argue that water acts as both agonist and antagonist to the enzymatic function. Our results indicate that the architecture of the two subdomains, most notably the strict conservation of key residues at the interface and within the (beta/alpha)(8) barrel, has been optimized to allow the efficient passage of ammonia, and not water, between the two remote active sites.
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Affiliation(s)
- Rommie E Amaro
- Department of Chemistry, University of Illinois, Urbana, Illinois, USA
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31
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Willemoës M, Mølgaard A, Johansson E, Martinussen J. Lid L11 of the glutamine amidotransferase domain of CTP synthase mediates allosteric GTP activation of glutaminase activity. FEBS J 2005; 272:856-64. [PMID: 15670165 DOI: 10.1111/j.1742-4658.2004.04525.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
GTP is an allosteric activator of CTP synthase and acts to increase the k(cat) for the glutamine-dependent CTP synthesis reaction. GTP is suggested, in part, to optimally orient the oxy-anion hole for hydrolysis of glutamine that takes place in the glutamine amidotransferase class I (GATase) domain of CTP synthase. In the GATase domain of the recently published structures of the Escherichia coli and Thermus thermophilus CTP synthases a loop region immediately proceeding amino acid residues forming the oxy-anion hole and named lid L11 is shown for the latter enzyme to be flexible and change position depending on the presence or absence of glutamine in the glutamine binding site. Displacement or rearrangement of this loop may provide a means for the suggested role of allosteric activation by GTP to optimize the oxy-anion hole for glutamine hydrolysis. Arg359, Gly360 and Glu362 of the Lactococcus lactis enzyme are highly conserved residues in lid L11 and we have analyzed their possible role in GTP activation. Characterization of the mutant enzymes R359M, R359P, G360A and G360P indicated that both Arg359 and Gly360 are involved in the allosteric response to GTP binding whereas the E362Q enzyme behaved like wild-type enzyme. Apart from the G360A enzyme, the results from kinetic analysis of the enzymes altered at position 359 and 360 showed a 10- to 50-fold decrease in GTP activation of glutamine dependent CTP synthesis and concomitant four- to 10-fold increases in K(A) for GTP. The R359M, R359P and G360P also showed no GTP activation of the uncoupled glutaminase reaction whereas the G360A enzyme was about twofold more active than wild-type enzyme. The elevated K(A) for GTP and reduced GTP activation of CTP synthesis of the mutant enzymes are in agreement with a predicted interaction of bound GTP with lid L11 and indicate that the GTP activation of glutamine dependent CTP synthesis may be explained by structural rearrangements around the oxy-anion hole of the GATase domain.
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Affiliation(s)
- Martin Willemoës
- Centre for Crystallographic Studies, Department of Chemistry, University of Copenhagen, Denmark.
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32
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Goto M, Omi R, Nakagawa N, Miyahara I, Hirotsu K. Crystal structures of CTP synthetase reveal ATP, UTP, and glutamine binding sites. Structure 2005; 12:1413-23. [PMID: 15296735 DOI: 10.1016/j.str.2004.05.013] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Revised: 03/10/2004] [Accepted: 05/14/2004] [Indexed: 01/28/2023]
Abstract
CTP synthetase (CTPs) catalyzes the last step in CTP biosynthesis, in which ammonia generated at the glutaminase domain reacts with the ATP-phosphorylated UTP at the synthetase domain to give CTP. Glutamine hydrolysis is active in the presence of ATP and UTP and is stimulated by the addition of GTP. We report the crystal structures of Thermus thermophilus HB8 CTPs alone, CTPs with 3SO4(2-), and CTPs with glutamine. The enzyme is folded into a homotetramer with a cross-shaped structure. Based on the binding mode of sulfate anions to the synthetase site, ATP and UTP are computer modeled into CTPs with a geometry favorable for the reaction. Glutamine bound to the glutaminase domain is situated next to the triad of Glu-His-Cys as a catalyst and a water molecule. Structural information provides an insight into the conformational changes associated with the binding of ATP and UTP and the formation of the GTP binding site.
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Affiliation(s)
- Masaru Goto
- Department of Chemistry, Graduate School of Science, Osaka University, Osaka 560-0043, Japan
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33
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Kothe M, Purcarea C, Guy HI, Evans DR, Powers-Lee SG. Direct demonstration of carbamoyl phosphate formation on the C-terminal domain of carbamoyl phosphate synthetase. Protein Sci 2004; 14:37-44. [PMID: 15576558 PMCID: PMC2253338 DOI: 10.1110/ps.041041305] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Carbamoyl phosphate synthetase synchronizes the utilization of two ATP molecules at duplicated ATP-grasp folds to catalyze carbamoyl phosphate formation. To define the dedicated functional role played by each of the two ATP sites, we have carried out pulse/labeling studies using the synthetases from Aquifex aeolicus and Methanococcus jannaschii, hyperthermophilic organisms that encode the two ATP-grasp folds on separate subunits. These studies allowed us to differentially label each active site with [gamma-(32)P]ATP and determine the fate of the labeled gamma-phosphate in the synthetase reaction. Our results provide the first direct demonstration that enzyme-catalyzed transfer of phosphate from ATP to carbamate occurs on the more C-terminal of the two ATP-grasp folds. These findings rule out one mechanism proposed for carbamoyl phosphate synthetase, where one ATP acts as a molecular switch, and provide additional support for a sequential reaction mechanism where the gamma-phosphate groups of both ATP molecules are transferred to reactants. CP synthesis by subunit C in our single turnover pulse/chase assays did not require subunit N, but subunit N was required for detectable CP synthesis in the traditional continuous assay. These findings suggest that cross-talk between domain N and C is required for product release from subunit C.
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Affiliation(s)
- Michael Kothe
- Department of Biology, Northeastern University, Boston, MA 02115, USA
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34
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Amaro R, Luthey-Schulten Z. Molecular dynamics simulations of substrate channeling through an α–β barrel protein. Chem Phys 2004. [DOI: 10.1016/j.chemphys.2004.05.019] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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35
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Endrizzi JA, Kim H, Anderson PM, Baldwin EP. Crystal structure of Escherichia coli cytidine triphosphate synthetase, a nucleotide-regulated glutamine amidotransferase/ATP-dependent amidoligase fusion protein and homologue of anticancer and antiparasitic drug targets. Biochemistry 2004; 43:6447-63. [PMID: 15157079 PMCID: PMC2891762 DOI: 10.1021/bi0496945] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cytidine triphosphate synthetases (CTPSs) produce CTP from UTP and glutamine, and regulate intracellular CTP levels through interactions with the four ribonucleotide triphosphates. We solved the 2.3-A resolution crystal structure of Escherichia coli CTPS using Hg-MAD phasing. The structure reveals a nearly symmetric 222 tetramer, in which each bifunctional monomer contains a dethiobiotin synthetase-like amidoligase N-terminal domain and a Type 1 glutamine amidotransferase C-terminal domain. For each amidoligase active site, essential ATP- and UTP-binding surfaces are contributed by three monomers, suggesting that activity requires tetramer formation, and that a nucleotide-dependent dimer-tetramer equilibrium contributes to the observed positive cooperativity. A gated channel that spans 25 A between the glutamine hydrolysis and amidoligase active sites provides a path for ammonia diffusion. The channel is accessible to solvent at the base of a cleft adjoining the glutamine hydrolysis active site, providing an entry point for exogenous ammonia. Guanine nucleotide binding sites of structurally related GTPases superimpose on this cleft, providing insights into allosteric regulation by GTP. Mutations that confer nucleoside drug resistance and release CTP inhibition map to a pocket that neighbors the UTP-binding site and can accommodate a pyrimidine ring. Its location suggests that competitive feedback inhibition is affected via a distinct product/drug binding site that overlaps the substrate triphosphate binding site. Overall, the E. coli structure provides a framework for homology modeling of other CTPSs and structure-based design of anti-CTPS therapeutics.
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Affiliation(s)
| | | | | | - Enoch P. Baldwin
- Corresponding author. . Phone: (530) 752–1108. Fax: (530) 752–3085
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36
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Nobeli I, Ponstingl H, Krissinel EB, Thornton JM. A Structure-based Anatomy of the E.coli Metabolome. J Mol Biol 2003; 334:697-719. [PMID: 14636597 DOI: 10.1016/j.jmb.2003.10.008] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The Escherichia coli metabolome has been characterised using the two-dimensional structures of 745 metabolites, obtained from the EcoCyc and KEGG databases. Physicochemical properties of the metabolome have been calculated to provide an overview of this set of cognate ligands. A library of fragments commonly found among these molecules has been employed to reveal the main constituents of metabolites, and to assist a broad classification of the metabolome into biochemically relevant classes. Fragment-based fingerprints reveal the metabolome as a continuum in the two-dimensional structural space, where clusters of molecules sharing similar scaffolds can be identified, but are generally overlapping. Nucleotide, carbohydrate and amino acid-like molecules are the most prominent, but at high levels of similarity, a more detailed classification is possible. Classification schemes for the metabolome are a promising tool for understanding the chemical diversity of the metabolome. When used in conjunction with existing classifications of the proteome, they can help to elucidate the binding preferences and promiscuity of proteins and their cognate substrates.
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Affiliation(s)
- Irene Nobeli
- EMBL-European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SD, UK.
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37
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Sakai H, Vassylyeva MN, Matsuura T, Sekine SI, Gotoh K, Nishiyama M, Terada T, Shirouzu M, Kuramitsu S, Vassylyev DG, Yokoyama S. Crystal structure of a lysine biosynthesis enzyme, LysX, from Thermus thermophilus HB8. J Mol Biol 2003; 332:729-40. [PMID: 12963379 DOI: 10.1016/s0022-2836(03)00946-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The thermophilic bacterium Thermus thermophilus synthesizes lysine through the alpha-aminoadipate pathway, which uses alpha-aminoadipate as a biosynthetic intermediate of lysine. LysX is the essential enzyme in this pathway, and is believed to catalyze the acylation of alpha-aminoadipate. We have determined the crystal structures of LysX and its complex with ADP at 2.0A and 2.38A resolutions, respectively. LysX is composed of three alpha+beta domains, each composed of a four to five-stranded beta-sheet core flanked by alpha-helices. The C-terminal and central domains form an ATP-grasp fold, which is responsible for ATP binding. LysX has two flexible loop regions, which are expected to play an important role in substrate binding and protection. In spite of the low level of sequence identity, the overall fold of LysX is surprisingly similar to that of other ATP-grasp fold proteins, such as D-Ala:D-Ala ligase, PurT-encoded glycinamide ribonucleotide transformylase, glutathione synthetase, and synapsin I. In particular, they share a similar spatial arrangement of the amino acid residues around the ATP-binding site. This observation strongly suggests that LysX is an ATP-utilizing enzyme that shares a common evolutionary ancestor with other ATP-grasp fold proteins possessing a carboxylate-amine/thiol ligase activity.
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Affiliation(s)
- Hiroaki Sakai
- RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama, 230-0045, Japan
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38
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Abstract
Recently, an alternative has been offered to the concept of transition state (TS) stabilization as an explanation for rate enhancements in enzyme-catalyzed reactions. Instead, most of the rate increase has been ascribed to preorganization of the enzyme active site to bind substrates in a geometry close to that of the TS, which then transit the activation barrier impelled by motions along the reaction coordinate. The question as to how an enzyme achieves such preorganization and concomitant TS stabilization as well as potential coupled motions along the reaction coordinate leads directly to the role of protein dynamic motion. Dihydrofolate reductase (DHFR) is a paradigm in which the role of dynamics in catalysis continues to be unraveled by a wealth of kinetic, structural, and computational studies. DHFR has flexible loop regions adjacent to the active site whose motions modulate passage through the kinetically preferred pathway. The participation of residues distant from the DHFR active site in enhancing the rate of hydride transfer, however, is unanticipated and may signify the importance of long range protein motions. The general significance of protein dynamics in understanding other biological processes is briefly discussed.
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Affiliation(s)
- P T Ravi Rajagopalan
- Department of Chemistry, Pennsylvania State University, University Park, 16802, USA
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39
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Amaro R, Tajkhorshid E, Luthey-Schulten Z. Developing an energy landscape for the novel function of a (beta/alpha)8 barrel: ammonia conduction through HisF. Proc Natl Acad Sci U S A 2003; 100:7599-604. [PMID: 12799468 PMCID: PMC164632 DOI: 10.1073/pnas.1331150100] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
HisH-hisF is a multidomain globular protein complex; hisH is a class I glutamine amidotransferase that hydrolyzes glutamine to form ammonia, and hisF is a (beta/alpha)8 barrel cyclase that completes the ring formation of imidizole glycerol phosphate synthase. Together, hisH and hisF form a glutamine amidotransferase that carries out the fifth step of the histidine biosynthetic pathway. Recently, it has been suggested that the (beta/alpha)8 barrel participates in a novel function: to channel ammonia from the active site of hisH to the active site of hisF. The present study presents a series of molecular dynamic simulations that investigate the channeling function of hisF. This article reconstructs potentials of mean force for the conduction of ammonia through the channel, and the entrance of ammonia through the strictly conserved channel gate, in both a closed and a hypothetical open conformation. The resulting energy landscape within the channel supports the idea that ammonia does indeed pass through the barrel, interacting with conserved hydrophilic residues along the way. The proposed open conformation, which involves an alternate rotamer state of one of the gate residues, presents only an approximately 2.5-kcal energy barrier to ammonia entry. Another alternate open-gate conformation, which may play a role in non-nitrogen-fixing organisms, is deduced through bioinformatics.
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Affiliation(s)
- Rommie Amaro
- Department of Chemistry and Theoretical and Computational Biophysics Group, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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40
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Schnizer HG, Boehlein SK, Stewart JD, Richards NGJ, Schuster SM. gamma-Glutamyl thioester intermediate in glutaminase reaction catalyzed by Escherichia coli asparagine synthetase B. Methods Enzymol 2003; 354:260-71. [PMID: 12418233 DOI: 10.1016/s0076-6879(02)54022-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Affiliation(s)
- Holly G Schnizer
- Department of Biochemistry, University of Florida College of Medicine, Gainesville, Florida 32610, USA
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41
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Thoden JB, Huang X, Raushel FM, Holden HM. Carbamoyl-phosphate synthetase. Creation of an escape route for ammonia. J Biol Chem 2002; 277:39722-7. [PMID: 12130656 DOI: 10.1074/jbc.m206915200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Carbamoyl-phosphate synthetase catalyzes the production of carbamoyl phosphate through a reaction mechanism requiring one molecule of bicarbonate, two molecules of MgATP, and one molecule of glutamine. The enzyme from Escherichia coli is composed of two polypeptide chains. The smaller of these belongs to the Class I amidotransferase superfamily and contains all of the necessary amino acid side chains required for the hydrolysis of glutamine to glutamate and ammonia. Two homologous domains from the larger subunit adopt conformations that are characteristic for members of the ATP-grasp superfamily. Each of these ATP-grasp domains contains an active site responsible for binding one molecule of MgATP. High resolution x-ray crystallographic analyses have shown that, remarkably, the three active sites in the E. coli enzyme are connected by a molecular tunnel of approximately 100 A in total length. Here we describe the high resolution x-ray crystallographic structure of the G359F (small subunit) mutant protein of carbamoyl phosphate synthetase. This residue was initially targeted for study because it resides within the interior wall of the molecular tunnel leading from the active site of the small subunit to the first active site of the large subunit. It was anticipated that a mutation to the larger residue would "clog" the ammonia tunnel and impede the delivery of ammonia from its site of production to the site of utilization. In fact, the G359F substitution resulted in a complete change in the conformation of the loop delineated by Glu-355 to Ala-364, thereby providing an "escape" route for the ammonia intermediate directly to the bulk solvent. The substitution also effected the disposition of several key catalytic amino acid side chains in the small subunit active site.
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Affiliation(s)
- James B Thoden
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin, 53706-1544, USA
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42
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Li H, Ryan TJ, Chave KJ, Van Roey P. Three-dimensional structure of human gamma -glutamyl hydrolase. A class I glatamine amidotransferase adapted for a complex substate. J Biol Chem 2002; 277:24522-9. [PMID: 11953431 DOI: 10.1074/jbc.m202020200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
gamma-Glutamyl hydrolase catalyzes the cleavage of the gamma-glutamyl chain of folylpoly-gamma-glutamyl substrates and is a central enzyme in folyl and antifolyl poly-gamma-glutamate metabolism. The crystal structure of human gamma-glutamyl hydrolase, determined at 1.6-A resolution, reveals that the protein is a homodimer. The overall structure of human gamma-glutamyl hydrolase contains 11 alpha-helices and 14 beta-strands, with a fold in which a central eight-stranded beta-sheet is sandwiched by three and five alpha-helices on each side. The topology is very similar to that of the class I glutamine amidotransferase domains, with the only major differences consisting of extensions in four loops and at the C terminus. These insertions are important for defining the substrate binding cleft and/or the dimer interface. Two sequence motifs are found in common between human gamma-glutamyl hydrolase and the class I glutamine amidotransferase family and include the catalytically essential residues, Cys-110 and His-220. These residues are located in the center of a large l-shaped cleft that is closed at one end and open at the other. Several conserved residues, including Glu-114, His-171, Gln-218, and Lys-223, may be important for substrate binding. Modeling of a methotrexate thioester intermediate, based on the corresponding complex of the glutamate thioester intermediate of Escherichia coli carbamoyl-phosphate synthetase, indicates that the substrate binds in an orientation with the pteroyl group toward the open end of the cleft.
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Affiliation(s)
- Hongmin Li
- Division of Molecular Medicine, Wadsworth Center, Albany, New York 12201-0509, USA
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43
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Abstract
Within the ever-expanding repertoire of known protein sequences and structures, many examples of evolving three-dimensional structures are emerging that illustrate the plasticity and robustness of protein folds. The mechanisms by which protein folds change often include the fusion of duplicated domains, followed by divergence through mutation. Such changes reflect both the stability of protein folds and the requirements of protein function.
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Affiliation(s)
- Lisa N Kinch
- Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9050, USA.
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44
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Miles BW, Thoden JB, Holden HM, Raushel FM. Inactivation of the amidotransferase activity of carbamoyl phosphate synthetase by the antibiotic acivicin. J Biol Chem 2002; 277:4368-73. [PMID: 11729189 DOI: 10.1074/jbc.m108582200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Carbamoyl phosphate synthetase (CPS) from Escherichia coli catalyzes the formation of carbamoyl phosphate from 2 mol of ATP, bicarbonate, and glutamine. CPS was inactivated by the glutamine analog, acivicin. In the presence of ATP and bicarbonate the second-order rate constant for the inactivation of the glutamine-dependent activities was 4.0 x 10(4) m(-1) s(-1). In the absence of ATP and bicarbonate the second-order rate constant for inactivation of CPS was reduced by a factor of 200. The enzyme was protected against inactivation by the inclusion of glutamine in the reaction mixture. The ammonia-dependent activities were unaffected by the incubation of CPS with acivicin. These results are consistent with the covalent labeling of the glutamine-binding site located within the small amidotransferase subunit. The binding of ATP and bicarbonate to the large subunit of CPS must also induce a conformational change within the amidotransferase domain of the small subunit that enhances the nucleophilic character of the thiol group required for glutamine hydrolysis. The acivicin-inhibited enzyme was crystallized, and the three-dimensional structure was determined by x-ray diffraction techniques. The thiol group of Cys-269 was covalently attached to the dihydroisoxazole ring of acivicin with the displacement of a chloride ion.
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Affiliation(s)
- Bryant W Miles
- Department of Chemistry, Texas A & M University, College Station, Texas 77842-3012, USA
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45
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Chaudhuri BN, Lange SC, Myers RS, Chittur SV, Davisson V, Smith JL. Crystal Structure of Imidazole Glycerol Phosphate Synthase. Structure 2001. [DOI: 10.1016/s0969-2126(01)00661-x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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46
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Decicco CP, Nelson DJ, Luo Y, Shen L, Horiuchi KY, Amsler KM, Foster LA, Spitz SM, Merrill JJ, Sizemore CF, Rogers KC, Copeland RA, Harpel MR. Glutamyl-gamma-boronate inhibitors of bacterial Glu-tRNA(Gln) amidotransferase. Bioorg Med Chem Lett 2001; 11:2561-4. [PMID: 11549469 DOI: 10.1016/s0960-894x(01)00499-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Analogues of glutamyl-gamma-boronate (1) were synthesized as mechanism-based inhibitors of bacterial Glu-tRNA(Gln) amidotransferase (Glu-AdT) and were designed to engage a putative catalytic serine nucleophile required for the glutaminase activity of the enzyme. Although 1 provides potent enzyme inhibition, structure-activity studies revealed a narrow range of tolerated chemical changes that maintained activity. Nonetheless, growth inhibition of organisms that require Glu-AdT by the most potent enzyme inhibitors appears to validate mechanism-based inhibitor design of Glu-AdT as an approach to antimicrobial development.
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Affiliation(s)
- C P Decicco
- Department of Medicinal Chemistry, DuPont Pharmaceuticals Company, Experimental Station, PO Box 80400, Wilmington, DE 19880, USA.
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Beismann-Driemeyer S, Sterner R. Imidazole glycerol phosphate synthase from Thermotoga maritima. Quaternary structure, steady-state kinetics, and reaction mechanism of the bienzyme complex. J Biol Chem 2001; 276:20387-96. [PMID: 11264293 DOI: 10.1074/jbc.m102012200] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Imidazole glycerol phosphate synthase, which links histidine and de novo purine biosynthesis, is a member of the glutamine amidotransferase family. In bacteria, imidazole glycerol phosphate synthase constitutes a bienzyme complex of the glutaminase subunit HisH and the synthase subunit HisF. Nascent ammonia produced by HisH reacts at the active site of HisF with N'-((5'-phosphoribulosyl)formimino)-5-aminoimidazole-4-carboxamide-ribonucleotide to yield the products imidazole glycerol phosphate and 5-aminoimidazole-4-carboxamide ribotide. In order to elucidate the interactions between HisH and HisF and the catalytic mechanism of the HisF reaction, the enzymes tHisH and tHisF from Thermotoga maritima were produced in Escherichia coli, purified, and characterized. Isolated tHisH showed no detectable glutaminase activity but was stimulated by complex formation with tHisF to which either the product imidazole glycerol phosphate or a substrate analogue were bound. Eight conserved amino acids at the putative active site of tHisF were exchanged by site-directed mutagenesis, and the purified variants were investigated by steady-state kinetics. Aspartate 11 appeared to be essential for the synthase activity both in vitro and in vivo, and aspartate 130 could be partially replaced only by glutamate. The carboxylate groups of these residues could provide general acid/base catalysis in the proposed catalytic mechanism of the synthase reaction.
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Affiliation(s)
- S Beismann-Driemeyer
- Universität zu Köln, Institut für Biochemie, Otto-Fischer-Str. 12-14, D-50674 Köln, Germany
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Spraggon G, Kim C, Nguyen-Huu X, Yee MC, Yanofsky C, Mills SE. The structures of anthranilate synthase of Serratia marcescens crystallized in the presence of (i) its substrates, chorismate and glutamine, and a product, glutamate, and (ii) its end-product inhibitor, L-tryptophan. Proc Natl Acad Sci U S A 2001; 98:6021-6. [PMID: 11371633 PMCID: PMC33415 DOI: 10.1073/pnas.111150298] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/27/2001] [Indexed: 11/18/2022] Open
Abstract
The crystal structure of anthranilate synthase (AS) from Serratia marcescens, a mesophilic bacterium, has been solved in the presence of its substrates, chorismate and glutamine, and one product, glutamate, at 1.95 A, and with its bound feedback inhibitor, tryptophan, at 2.4 A. In comparison with the AS structure from the hyperthermophile Sulfolobus solfataricus, the S. marcescens structure shows similar subunit structures but a markedly different oligomeric organization. One crystal form of the S. marcescens enzyme displays a bound pyruvate as well as a putative anthranilate (the nitrogen group is ambiguous) in the TrpE subunit. It also confirms the presence of a covalently bound glutamyl thioester intermediate in the TrpG subunit. The tryptophan-bound form reveals that the inhibitor binds at a site distinct from that of the substrate, chorismate. Bound tryptophan appears to prevent chorismate binding by a demonstrable conformational effect, and the structure reveals how occupancy of only one of the two feedback inhibition sites can immobilize the catalytic activity of both TrpE subunits. The presence of effectors in the structure provides a view of the locations of some of the amino acid residues in the active sites. Our findings are discussed in terms of the previously described AS structure of S. solfataricus, mutational data obtained from enteric bacteria, and the enzyme's mechanism of action.
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Affiliation(s)
- G Spraggon
- Genomics Institute of the Novartis Research Foundation, 3115 Merryfield Row, La Jolla, CA 92121-1115, USA
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Bearne SL, Hekmat O, Macdonnell JE. Inhibition of Escherichia coli CTP synthase by glutamate gamma-semialdehyde and the role of the allosteric effector GTP in glutamine hydrolysis. Biochem J 2001; 356:223-32. [PMID: 11336655 PMCID: PMC1221831 DOI: 10.1042/0264-6021:3560223] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cytidine 5'-triphosphate synthase catalyses the ATP-dependent formation of CTP from UTP with either ammonia or glutamine as the source of nitrogen. When glutamine is the substrate, GTP is required as an allosteric effector to promote catalysis. Escherichia coli CTP synthase, overexpressed as a hexahistidine-tagged form, was purified to high specific activity with the use of metal-ion-affinity chromatography. Unfused CTP synthase, generated by the enzymic removal of the hexahistidine tag, displayed an activity identical with that of the purified native enzyme and was used to study the effect of GTP on the inhibition of enzymic activity by glutamate gamma-semialdehyde. Glutamate gamma-semialdehyde is expected to inhibit CTP synthase by reacting reversibly with the active-site Cys-379 to form an analogue of a tetrahedral intermediate in glutamine hydrolysis. Indeed, glutamate gamma-semialdehyde is a potent linear mixed-type inhibitor of CTP synthase with respect to glutamine (K(is) 0.16+/-0.03 mM; K(ii) 0.4+/-0.1 mM) and a competitive inhibitor with respect to ammonia (K(i) 0.39+/-0.06 mM) in the presence of GTP at pH 8.0. The mutant enzyme (C379A), which is fully active with ammonia but has no glutamine-dependent activity, is not inhibited by glutamate gamma-semialdehyde. Although glutamate gamma-semialdehyde exists in solution primarily in its cyclic form, Delta(1)-pyrroline-5-carboxylate, the variation of inhibition with pH, and the weak inhibition by cyclic analogues of Delta(1)-pyrroline-5-carboxylate (L-proline, L-2-pyrrolidone and pyrrole-2-carboxylate) confirm that the rare open-chain aldehyde species causes the inhibition. When ammonia is employed as the substrate in the absence of GTP, the enzyme's affinity for glutamate gamma-semialdehyde is decreased approx. 10-fold, indicating that the allosteric effector, GTP, functions by stabilizing the protein conformation that binds the tetrahedral intermediate(s) formed during glutamine hydrolysis.
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Affiliation(s)
- S L Bearne
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4H7, Canada.
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O'Donoghue P, Amaro RE, Luthey-Schulten Z. On the structure of hisH: protein structure prediction in the context of structural and functional genomics. J Struct Biol 2001; 134:257-68. [PMID: 11551184 DOI: 10.1006/jsbi.2001.4390] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We predict a structure of the glutamine amidotransferase subunit (hisH) of imidazole glycerol phosphate synthase (IGPS) which catalyzes the fifth step of the histidine biosynthesis in Escherichia coli. The model is constructed using an energy-based threading program augmented by a multiple sequence to structure profile analysis. In developing our model we identified a conserved core region within hisH and a variable domain which is the likely site of interaction with the synthase subunit (hisF) of IGPS. Information available from structural and functional genomics studies was used to improve the structure prediction, to discuss parallels between histidine biosynthesis and other amino acid and nucleotide metabolic pathways, and to better understand the protein-protein interactions between the hisH and hisF domains of IGPS. This work allows us to develop a preliminary model for the structure of the entire IGPS holoenzyme.
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Affiliation(s)
- P O'Donoghue
- School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, USA
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